Saturday, March 13, 2010

"Finished" Version 3

Version 3 is basically finished.
Will give a quick overview of how it has turned out.

Overall I am pretty happy with the case construction. Having a plastic base as well as top case gives a good solid feel about it.

The top case is as for the last version, with the top and sides glued together.
The case is a lot shorter than the last one, no room for air to circulate above the fan. Needs to pull in the air from outside - and hence the vent.
I have attached both the HD and the CPU fan to the case... not sure if this is a good idea or not.

For the base, this is now a sheet of perspex, with little raised lumps onto which the mother board is screwed. I have embedded a nut in each raise lump into which the motherboard screw goes into.
The base also has the vents cut around the edges for the air flow to exit. At the front of the base is a piece of perspex into which the HD and Power LEDs are pushed.

The box fits together nicely...

At the top back I have attached some plastic guides so that the metal back plate nicely slides into the channel cut into the top piece of perspex.
On the bottom of the case I have just stuck some felt 'feet' to raise the box off the table, and ensure some air can flow out.

The HD and CPU fan attach into the case using round elastic. The idea is that this can help reduce any vibration that transfers to the case.
I think it works OK for the HD, but not for the Fan. For the fan would ideally put some rubber mounting feet to keep the fan from pushing up against the case too firmly.

A Chinese knockoff Pico Power Supply has been used.

It is *just* short enough to clear the top of the case.
Got it here from (the Chinese equivalent of ebay) for 249 RMB. Is a 150W supply, but only with a 120W adapter.

With all the electronics in place, including the Capacitive on/off switch, it looks like this.

Note that comfortable with the wiring... bit of a hassle with ensuring that the cabling handles the lid being removed, and falls nicely into place when the lid is fitted.

Closing the case together, the back metal plate fits securely into the channels in the top and bottom sheets of the case.

Metal work is not my forte :-)

All in all, has the best feel of all the boxes so far.
Fan noise is a bit of an issue at the moment. It is using the 2000 RPM Scythe slim fan. It is running at full speed all the time. Speedfan no longer seems to work for me with Windows 7, so cannot slow it down. I am thinking of building a physical speed controller for the fan, along the lines outlined here.
The fan seems to be quite capable of sucking in a good amount of air to keep the CPU cool - there is noticeable airflow out of the box on all sides from the holes underneath.

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Capacitive On-Off Switch

I dont really like the idea of cutting a hole in the perspex case for mounting a switch. And besides, most computer momentary switches that you find are pretty plain.

So - for the box I will be using a capacitive proximity sensor to turn it on/off.
One of the easiest to find here in China is one of those industrial devices - see below for the one I am using.

Not the smallest thing in the world - however there is not too much of an issue with space around the area where I will be mounting it.

This capacitive switch cost around 35 RMB, which is around 5 USD ??
It has a sensing distance of around 8mm, and works OK through the perspex. Not sure how well it would work through other plastic types, but Perspex is OK.

This is a 12 V device, so it needs to be run directly from the 12V power supply. As it is a 12 V thing, cannot just directly connect it to the motherboard and expect not to have some problems. The switched connection floats up to 12V when not active, so connecting this to the 5V-related on/off pins on the motherboard is probably not a good idea.

So I also grabbed a 12V Reed Relay - to give some isolation. The relay is in a SIP package - so I wired it into the lead of the sensor - can see the lump in the cable in the above diagram.

I mounted the switch so it was at the side of the case towards the front. Reason for this is that others kept suggesting it was a bad idea to capacitive sense - what happens if a cat walks past too close ??
So i figured that if it was on the side, this would not be exposed to places that cats would walk.

So when in place, the case basically just slides down over the top, with the capacitive sensor roughly flush against the inside of the case.
Now when you want to start the PC, you basically rest your hand on the side of the box for a brief moment, and it fires up. Can also turn the PC off.

There are various other capacitive sensing products out there - would be nice if I had the spare time to investigate them... later maybe.

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Sunday, January 31, 2010

TV Card

There should be enough room in this box for a TV card. Will have to be a PCIe X1 card... I have an AverMedia one.

To keep it within the box height, I will be using a PCIe right angle adapter - as shown

The back of the box will be a metal plate - held between the top and bottom sheets of perspex by sliding into slots in those sheets. Not the easiest to get in - but seems to make the sheet of metal reasonably stiff.

The main difficulty with putting the TV card in on the right angled attachment card is - that there is no simple way that I can see of firmly attaching it to the back plate. It needs to be firmly attached to handle the plugging in and out of the antenna cable.

(Note that I chopped off the top and bottom ends of the normal mounting bracket - too long.)
I cannot see how I can simply screw or attach the card to the back plate - not easy to create new screw holes in the mounting plate piece that remains... and there is not going to be too much room left on the back metal sheet either.

The only option that I could think of was to create a separate 'frame' out of a sheet of perspex. This 'frame' would hold the card firm in the vertical direction, and rest against the motherboard at the bottom to resist the forces of insertion of the TV cable. The frame would be mounted inside the back metal plate - so no issues when pulling out the TV cable.
Here is the basic 'frame' before finishing it up a bit.

To fit the 'frame' to the TV card, you need to unscrew the attachment plate, then re-assemble it with the 'frame' between the attachment plate and the TV card...
A picture probably makes it a little easier to understand...

Note that the perspex is around 4.5 mm thick - too thick to go between the motherboard and the back metal plate - so I needed to cut a channel to allow for the motherboard. Now when you push in against the TV card, the force is taken against the motherboard, and will have to also be matched with some support on the top edge of the 'frame' - will manage that later within the case.

Anyway - this frame idea seems to work. Not sure if it is generic enough to be useable with other TV cards...
I think it also could be refined a little - and maybe better if it was someone integrated with the back metal plate instead of requiring a separate 'frame'.

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